There has been a marked tendency in recent years for highly versatile cameras using exchangeable lenses (hereinafter called lens exchangeble cameras) to have a selectable plurality of automatic exposure control modes for increasing the exposure functions available to the camera operator. While such functional enhancement or improvement is itself welcome, at the same time, it increases the number of necessary operating steps for photographic preparations, thereby resulting in increased difficulty for camera operators, and especially inexperienced camera operators.
For example, lens exchangeable cameras have been proposed which can optionally be set either to an aperture priority automatic shutter speed control mode, a shutter speed priority automatic aperture control mode or an automatic programmed exposure control mode. With these types of cameras, a mode changeover is made possible by setting a diaphragm presetting means, provided on an exchangeable lens, to an AUTO position, and by setting a mode selector lever, provided on the camera body, to any required MODE position. Moreover, setting a dial provided on the camera body to an f-number or a shutter speed to be preferentially set, or to a programmed position, is required to photograph in an actually selected mode. Such a lens exchangeable camera is described at pages 68 and 69 of the Japanese Publication, PHOTOGRAPHIC INDUSTRIES, published on June 1, 1978.
Additionally, U.S. Pat. No 4,167,313 describes camera apparatus using an electromagnetic diaphragm mechanism that is optionally settable by the camera operator to one of four photographing modes, including manual photography, automatic photography with a preset diaphragm aperture, automatic photography with a preset exposure period, and automatic programmed photography.
In the automatic photographic mode with preset diaphragm aperture (diaphragm aperture priority) a mode selection knob is manually turned until an indication "AA" is aligned with an index to establish the necessary setting of an arrangement of mode selection switches. The camera operator is also required to set the diaphragm setting by manual rotation of a diaphragm setting ring. In the automatic, programmed photographic mode, the mode selection knob is turned until an indication "PA" is aligned with the associated index. The camera operator is also required to operate a "programmed condition changeover knob", to complete the setting of this operational mode.